1. Field of the Invention
This invention generally relates to semiconductor fabrication processes and, more particularly, to a high-density Germanium-on-insulator (GOI) photodiode.
2. Description of the Related Art
FIG. 1 is a Cross-Sectional Transmission Electron Microscopy (XTEM) image of an interface between Germanium (Ge) and Si3N4. The Ge film has been regrown by liquid phase epitaxy. In a copending application entitled METHOD OF EPITAXIAL GROWTH OF GERMANIUM PHOTODETECTOR FOR CMOS IMAGER, invented by Lee et al., a method for growing single crystalline Ge film by liquid phase epitaxy is presented, along with a means of fabricating a PIN photo detector for infrared photon detection. However, it is noted that the interface between Ge single crystal and the bottom dielectric layer (Si3N4) is not perfect, as shown in the TEM image. This interface may potentially cause leakage current in the diode. This interface is likely the result of the Ge PIN diode using the entire Ge film, so that the bottom interface degrades the electrical performance.
It has also proven difficult to form a dense array of Ge-on-silicon photodiode structures. A diode structure with a high-density yield would be beneficial for CMOS imager fabrication. To that end, it would be beneficial if a Ge diode array could be fabricated with a minimum width isolation between diodes, corresponding to the minimum-sized features of a MOS transistor.